1. Field of the Invention
The present invention relates broadly to an apparatus for electrochemically processing water to modify the hydrogen ion concentration (pH) thereof and, more specifically, to an apparatus for electrolyzing water to produce alkaline and/or acidic water. In particular, the present invention is directed to improvements in a water electrolyzer of the continuous-flow membraneless type wherein alkaline water and acidic water generated by the electrolysis of water are separated from each other without recourse to the use of a membrane.
2. Description of the Prior Art
It is believed that hydroxyl ion (OH.sup.-) enriched alkaline water, which is often referred-to as "alkaline ion water", is useful in health maintenance when served as potable water as well as in accentuating taste when used in cooking or for the preparation of beverages such as tea and coffee. Similarly, hydrogen ion (H.sup.+) enriched acidic water is known as being useful for various purposes. For example, acidic water is suitable for boiling noodles and provides an astringent effect when applied to skin. More importantly, highly acidic water containing chlorine gas or hypochlorous acid, which results from the electrolysis of natural water containing sodium chloride or an aqueous solution of sodium chloride, presents a strong germicidal effect and therefore may be used for the purposes of sterilization and disinfection of bacteria.
To produce alkaline and/or acidic water, various types of water electrolyzer have been developed and marketed. As is well-known, water electrolyzers are designed to operate by making use of the water electrolysis process wherein, at the anode-water interface, OH.sup.- being present in water due to electrolytic dissociation of water molecules donates electron to the anode and is thereby oxidized into oxygen gas which is then removed away from the system. As a result, the H.sup.+ concentration is enhanced at the anode-water interface so that H.sup.+ enriched acidic water is resulted. In a similar manner, at the cathode-water interface, H.sup.+ accepts electron from the cathode and is reduced to hydrogen to form hydrogen gas which is similarly eliminated from the system so that the OH.sup.- concentration is increased at the cathode-water interface whereby OH.sup.- enriched alkaline water is generated. Further, when chlorine ion containing water such as natural water containing sodium chloride or an aqueous solution of sodium chloride is subjected to electrolysis, chlorine gas is formed at the anode-water interface and is partly dissolved into water in the form of hypochlorous acid to produce highly germicidal acidic water.
Earlier water electrolyzers have been designed to operate on the batch process. However, most of the modern water electrolyzers are of the continuous flow type. The continuous flow-type electrolyzers may be grouped into the "membrane" type and the "membraneless" type.
The membrane-type water electrolyzer is known, for example, from Japanese Utility Model Kokai Publication No. 56-80292, Japanese Patent Kokai Publication No. 58-189090 and Japanese Utility Model Kokoku Publication No. 58-47985. The membrane-type water electrolyzer includes an ion-permeable but water-impermeable membrane that is disposed in the flow path to separate a pair of electrodes from each other so as to prevent acidic water as generated along the anode from being mixed with alkaline water as produced along the cathode.
One of the problems associated with the membrane-type water electrolyzer is that the porous membrane provides a bed for bacteria and microorganism permitting them to breed when the electrolyzer is not in use. Another problem is that the membrane permits deposition of scales and deposits of water-insoluble substances such as calcium carbonate, calcium hydroxide and magnesium hydroxide. As these deposits are electrically insulating, the membrane clogged by the deposits increases the electric resistance across the electrolytic cell so that the efficiency of electrolysis is rapidly degraded.
To obviate these disadvantages, the membraneless-type water electrolyzer has been proposed in the art as disclosed, for example, in Japanese Patent Kokai Publication No. 4-284889 and Japanese Utility Model Kokai Publication No. 4-110189.
As shown, for example, in FIG. 3 of JP-4-284889, the membraneless electrolyzer is provided with a pair of electrodes which are positioned closely with one another to define therebetween a narrow flow path of a slit-shaped cross-section. The spacing between the electrode is generally less than 1 mm, usually in the order of 0.5 mm. As water to be electrolyzed is fed to flow through the narrow flow path, a laminar flow is established in the water flow under the action of viscosity acting upon the stationary surfaces of the flow path. Due to the formation of the laminar flow, acidic water generated by electrolysis at the anode-water interface flows along the anode surface without being mixed to any substantial degree with alkaline water produced at the cathode-water interface and flowing along the cathode surface. Advantageously, the membraneless electrolyzer is free from the foregoing problems involved in a membrane.
However, the problem associated with the membraneless electrolyzer is that it is extremely difficult to separate alkaline and acidic water from each other at the end of the flow path, because the flow path is very narrow (usually about 0.5 mm) and since the conventional membrane separating the electrodes has been eliminated.
JP-4-284889 proposes to separate acidic water from alkaline water by means of a baffle plate 14 protruding halfway into the downstream end of the flow path, as shown in FIG. 3 of this publication, the arrangement being such that the flow of acidic water which has flown along the anode surface impinges upon the baffle plate and is directed by the baffle plate toward an acidic water outlet.
Although this arrangement permits to separate acidic water from alkaline water to a certain degree without using the conventional membrane, it has been found that it is unable to selectively recover the thin layer of highly acidic water and strongly alkaline water flowing close to the electrodes. This is because the flow of water impinging upon the baffle plate generates an impermissible degree of turbulence which causes the layers of acidic and alkaline water so far separated in the laminar flow to be mixed with each other.